Body cavity embolism (e.g. brain blood vessel aneurysm occlusion by detachable coils, liquid embolism, particle embolism, balloon embolism) is a treatment that may have a high incidence of recurrence. Due to insufficient healing at the aneurysm/parent artery interface, mechanical and biological forces, incompletely understood, create a new expansion of aneurysm. That is the aneurysm reforms or recurs after endovascular, embolic treatment.
In one treatment Pt/Ir coils are packed in aneurysms so that they occupy ˜20% to 30% of the aneurysm volume and reduce the inflow of blood into the aneurysm. Aneurismal blood, at 70% to 80% by volume, clots by stagnation. Preferably, the clotted blood organizes and proceeds through a series of steps similar to those occurring at any wound in the body: (1) hemostasis, (2) inflammation, (3) tissue formation, and (4) remodeling. An aneurysm so treated is excluded from the arterial circulation. On the other hand, for partially understood reasons, the clotted blood may not organize, the coil mass compacts and/or new blood flow—coupled with the diseased arterial tissue—allows expansion of the aneurysm. Thus the aneurysm recurs and remains susceptible to rupture and hemorrhagic stroke.
With the pursuit of tissue engineering, devices were created that attempt to direct or enhance the healing of the aneurysm/artery interface rather than rely on each patient's individual reaction to the embolism of the an aneurysm cavity. Embolic devices, such as electrolytically-detached Pt/Ir coils, have been designed with coatings that swell in aqueous solution or that provoke a mild inflammatory response.
One form of device contains a polyacrylamide hydrogel attached to the Pt/Ir detachable coil. As the coil resides in blood, the hydrogel swells and occupies more space than bare metal coils, leading to higher packing densities (˜40% to 50%).
Other coils use the biodegradable polymer PGLA (poly glycolyic/lactic acid—the same material used in absorbable sutures) as a bioactive coil coating to provoke a mild inflammatory response in the aneurysm that triggers aneurismal organization per the above wound healing steps.
Both approaches suffer from the same problem: they are limited by the small size of these coils and the fact that the coils must be delivered through a microcatheter with the smallest ID of ˜0.015″. Coils may have a minimum of 0.09 cm of surface area (0.01 1″ OD, over a 1 cm length). Placing a coating, hydrogel or bioactive coating, and ensuring that the treated coil can move through a 0.015″ ID catheter places a finite limit on the amount of hydrogel or bioactive coating applied to the coil. In general, the amount of material is limited by the surface of the coil and the delivery catheter. Limited to no efficacy data exist for the coated coils. However, physician feedback indicates that the results are no better than bare-metal coils.
Helical coils are one form of device that has been extensively employed. Hans Henkes, et al., NEUROSURGERY 54, No. 2, 268 (2004) describe the results of over 1800 procedures involving helical coils and conclude that such devices are safe and efficacious for occlusion for patients with intracranial aneurysms.
A number of variations on helical coils have been proposed heretofore. For example, U.S. Pat. No. 5,226,911 issued to Chee and Narient describes looping 5 to 100 biocompatible polymer fibers through the helical coils. Dacron, polyglycolic acid, polylactic acid, fluoropolymers, nylon and silk are among the polymers suggested for these fibers. U.S. Pat. No. 5,382,259 issued to Phelps and Van describes braided or woven fibrous tubular coverings with and without tassels for helical coils. U.S. Pat. No. 5,549,624 issued to Mirigian and Van describes a helical coil device with added fibrous loops which are described as increasing the device's thrombogenicity. U.S. Pat. No. 5,658,308 issued to Snyder describes a helical metal device with from one to several hundred axial fibrous strands passing through its center and optionally filaments attached to the windings of the coil. These filaments are recited to be bioactive or nonbioactive and to enhance the ability of the coil to occlude the site at which it is placed. U.S. Pat. No. 5,935,145 issued to Villar and Aganon describes helical coils two fibrous members, each of a different material, attached. One of the materials is preferably biodegradable. The other is preferably not biodegradable. U.S. Pat. No. 6,299,627 issued to Eder et al. describes devices with coils or braids and two coatings including an inner coating and another coating selected to affect the solubility of the inner coating.
All of this work suggests that although helical coil inserts are attractive vasoocclusive devices there are opportunities to improve their performance to achieve optimal performance in terms of ease of delivery to and placement at the treatment site and in terms of the degree and rate of vaso-occlusion achieved.